The long term aim of this project is to understand through visualization at molecular resolution, the molecular events that produce force in muscle contraction. The focus here is on striated muscle because mechanochemical coupling through the interaction of actin and myosin is best visualized within an organized filament system. Of all the striated muscles, the asynchronous insect flight muscle (IFM) of the large waterbug Lethocerus sp. reveals a particularly refined and ordered expression of the structures involved in force production. The crossbridge lattice of insect flight muscle (IFM) in mechanically defined structural states will be studied by 3-D image reconstruction using both tomographic and oblique section 3-D reconstruction methods. These mechanically defined states are produced using mixtures of AMPPNP and ethylene glycol in different proportions and at different temperatures. Mixtures of glycol and AMPPNP produce a graded change in the rigor tension and stiffness in IFM that have been hypothesized to take rigor crossbridges backward through the power stroke. Computer models will be generated of images and x-ray diagrams of IFM in different structural states. Modelling will encompass rigor as well as the different glycol-AMPPNP states studied as part of the 3-D reconstruction work. These models will be compared with experimental X-ray data and electron micrographs of IFM and acto-HMM to validate hypotheses of crossbridge arrangement and structure obtained by the 3-D reconstruction project.